1. Field of the Invention
The present invention relates to a photoelectric conversion device and, more particularly, to the device suitable for a facsimile apparatus, an image reader, a digital copying machine, or the like, which has a linear line sensor corresponding to the widthwise direction of an original, and reads image information while the original is moved relative to the linear line sensor.
2. Related Background Art
A known conventional photoelectric conversion device has an elongated linear line sensor (equal magnification type line sensor) has the same length as an original document width. The sensor is brought into direct contact with the original document. The sensor further does not require a focusing system or can reduce an operating distance of the focusing system. Such a conversion device can be utilized in a compact and low-cost machine.
In a known photoelectric conversion device having an equal magnification type line sensor which can reduce an operating distance of a focusing system, a convergence optical fiber or a contact lens array is used in the focusing system. In another known photoelectric conversion device having an equal magnification type line sensor which requires no focusing system, a line sensor is arranged on a transparent substrate, and light is irradiated onto an original surface from the rear surface side of the substrate. Light reflected by the original surface is then received on the line sensor.
An arrangement, wherein light incident from the rear surface side of the substrate is reflected and scattered by the original surface can be applied to a photoelectric conversion device with or without a focusing system. In particular, when the focusing system is omitted, since the original surface is brought perfectly into tight contact with the surface of the photoelectric conversion device, an advantage is that such an arrangement would be made more compact. In this arrangement, construction of light incident from the rear surface of the substrate is considered to be most preferable.
FIG. 1 shows a proximity conversion device which does not require a focusing system. FIG. 2 is a cross-sectional view taken along line A--A' in FIG. 1. An opening of a light-receiving window for a photoelectric conversion device S is indicated by W. The opening W of the window is defined by a closed hole formed in a first opaque layer formed on a glass substrate. However, in this related art, when the light-receiving window is formed, the following problems are posed.
(1) When the opaque layer is patterned in a hole shape by etching, an unetched portion is often formed in a hole forming portion of the hole-shaped closed pattern. Consequently, a hole having suitable shape and required size is rarely formed. Accordingly, as the area of the hole-shaped closed pattern is decreased, an unetched portion is formed more easily, which results in the original not being adequately illuminated. For example, in a proximity type linear-image sensor, when an A4-sized original is read at a density of 8 dots/mm, eight windows per mm are required. If the reading density is 16 dots/mm, sixteen windows twice the above case, are required. As the reading density is increased, it would be necessary that each window that is the area of the opening is reduced. As a result, etching errors occur more frequently, thus decreasing a yield.
(2) When the opaque layer formed on a large-area substrate is to be etched to form hole-shaped closed patterns, etching nonuniformity easily occurs. As the area of the substrate of the photoelectric conversion device is increased, an improvement of the yield cannot be expected.
In order to eliminate the unetched portion and etching nonuniformity, an etching method, that is a process that an etching solution mist is blown onto the substrate would be used. However, with this method, it is also difficult to etch all the windows uniformily. In mass-production, a special apparatus and special steps are required, resulting in poor mass-producibility and high cost.